A为什么错，为什么不能直接借？

问题如下：

Prior to 2007, banks would least likely finance their increasing investment holdings of U.S. dollar assets by:

选项：

A.

drawing on U.S. dollar bank credit lines.

B.

borrowing U.S. dollars from their central bank.

C.

borrowing U.S. dollars directly in the interbank markets.

D.

borrowing in their domestic currency and converting it to U.S. dollars in the spot market.

解释：

A银行可以通过以下方式为其日益增长的美元资产投资持有进行融资：一、在国内货币市场借款并将之在即期市场上转换成美元；二、直接在银行间市场、从其他市场参与者或从本国央行那里借入美元；三、银行还可以利用外汇掉期将其本币负债转换成美元，以便购买资产。